Field of the Invention
The present invention relates to a fuel cell module including a fuel cell stack formed by stacking a plurality of fuel cells for generating electrical energy by electrochemical reactions of a fuel gas and an oxygen-containing gas.
Description of the Related Art
In general, a solid oxide fuel cell (SOFC) employs a solid electrolyte. The solid electrolyte is an oxide ion conductor such as stabilized zirconia. The solid electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly (also referred to as MEA). The electrolyte electrode assembly is sandwiched between separators (bipolar plates). In use, generally, predetermined numbers of the electrolyte electrode assemblies and the separators are stacked together to form a fuel cell stack.
As the fuel gas supplied to the fuel cell, normally, a hydrogen gas produced from hydrocarbon raw material by a reformer has been used. In general, in the reformer, a reforming raw gas is obtained from a hydrocarbon raw fuel of a fossil fuel or the like, such as methane or LNG, and thereafter, the reforming raw gas undergoes partial oxidation reforming, steam reforming, or autothermal reforming, etc. to produce a reformed gas (fuel gas).
It is desired that this fuel cell is operated relatively at high temperature, and that the fuel cell has the heat insulating properties to improve the heat efficiency. A fuel cell system aimed to address this point has been proposed in Japanese Laid-Open Patent Publication No. 2012-182032. The fuel cell system has simple and compact structure with heat insulating properties while allowing a fuel cell stack to be heated uniformly.
This fuel cell system includes a fuel cell stack including a plurality of stacked fuel cells, a reformer, a heat exchanger, and a fuel cell stack mounting member for mounting the fuel cell stack. Further, the fuel cell system includes a fluid unit equipped with a frame member for holding the reformer, the heat exchanger, and the fuel cell stack mounting member. The fuel cell stack is provided on one side of the fluid unit, and a combustor is provided adjacent to the other side of the fluid unit. The combustor heats the reformer and the heat exchanger by the combustion gas produced in combustion.
Further, a first case member containing the fuel cell stack is connected to the fuel cell stack mounting member, and a second case member containing the first case member and the fluid unit are connected to the frame member.
Further, both ends of a channel member are connected to the fuel cell stack mounting member and the heat exchanger. An off gas which has been partially consumed in the power generation reaction of the fuel cell stack is supplied from an internal space of the first case member to the heat exchanger as a heating medium through the channel member. After heat exchange at the heat exchanger, the off gas discharged from the heat exchanger is discharged through an off gas channel formed between the first case member and the second case member.
As described above, the off gas discharged after partial consumption in the power generation reaction flows into the heat exchanger as a heating medium for heat exchange with an oxygen-containing gas before the oxygen-containing gas is supplied to the fuel cell stack. According to the disclosure, with the structure, the waste heat of the off gas can be collected effectively, and improvement in the heat efficiency is achieved easily. In particular, it becomes possible to utilize the waste heat for directly heating the fuel cells, and effectively utilize the waste heat as a heating energy for heating the oxygen-containing gas by the heat exchanger.